The present invention relates to crosslinked rubber particles, raft copolymer particles containing the crosslinked rubber particles and thermoplastic resin compositions containing these particles. More particularly, the invention relates to crosslinked rubber particles and graft copolymer particles, which can be used as impact resistant resins having excellent weatherability and heat stability or as impact modifiers, and to thermoplastic resin compositions containing these particles.
Crosslinked rubber particles and graft copolymer particles wherein vinyl monomers are graft-polymerized onto the crosslinked rubber particles, have been widely used as impact resistant resins or as impact modifiers.
As the impact resistant resins, there are well known, for example, a high impact polystyrene (HIPS) obtained by graft-polymerizing styrene onto polybutadiene particles, and an acrylonitrile-butadiene-styrene copolymer (ABS) obtained by graft-polymerizing acrylonitrile and styrene onto polybutadiene particles.
Known also as the impact modifier are an impact modifier (MBS resin) obtained by graft-polymerizing methyl methacrylate and styrene onto polybutadiene rubber particles or styrene-butadiene copolymer rubber particles, and a weathering resistant impact modifier obtained by graft-polymerizing methyl methacrylate onto acrylic rubber particles.
The reason why the crosslinked rubber particles as mentioned above have been widely used as an impact resistant resin or an impact modifier is that even if they pass through a molten state during molding processing, they can maintain the particle shape and therefore are easy to exhibit properties as designed. The above-mentioned impact modifiers obtained by using polybutadiene rubber particles have a high effect of improving impact resistance because the glass transition temperature (Tg) of polybutadiene is low. However, these modifiers have the problem of being thermally unstable and poor in weatherability because they have unsaturated bonds in their structure.
On the other hand, the above-mentioned impact modifier obtained by using acrylic rubber particles is superior in weatherability, but the effect of improving impact resistance is not so good because the Tg is higher than polybutadiene.
For the purpose of improving the above-mentioned defects, an impact modifier using particles of a polyorganosiloxane (silicone) rubber which has a lower Tg and an excellent weatherability, is proposed. For example, Japanese Patent Publication Kokai No. 60-252613 (Japanese Patent Publication Kokoku No. 6-29303) discloses a graft polymerization product of a vinyl monomer onto silicone rubber particles, and Japanese Patent Publication Kokai No. 64-6012 and Japanese Patent Publication Kokai No. 4-100812 disclose a graft polymerization product of a vinyl monomer onto a composite rubber composed of a polyorganosiloxane rubber component and a polyalkyl (meth)acrylate rubber component.
However, even such impact modifiers are not always satisfactory in impact resistance, particularly in low temperature impact resistance, so further improvement has been desired.
An object of the present invention is to provide crosslinked rubber particles and graft copolymer particles containing the crosslinked rubber particles, which can be used as an impact resistant resin or impact modifier having a remarkably improved impact resistance, particularly low temperature impact resistance.